Variable condenser



April 28, 1942.

VARIABLE CONDENSER Filed June 28, 1939 2 Sheets-Sheet 1 INVENTORS FRANKLIN AND fg. E.

YTON THURNE www ATTORNEY.

April 28, 1942.

R. E. FRANKLIN ETAL 2,281,147

VARIABLE CONDENSER Filed June 28, 1959 2 Sheets-Sheet 2 40a 36 326 g: 3f 33 39a 39 37a] Y Ilrl 32a 32h ISS L3.? L57 40 HHII HHH a l 3a 35a INVENTORS By E YTN THOR/VE ATTORNEY.

Patented Apr. 28, 1942 VARIABLE CONDENSER Ralph E. Franklin and Earle Dayton Thorne,

Patchogue, N. Y., assignors to Radio Corporation of America, a corporation of Delaware Application June 28, 1939, Serial No. 281,642

1 Claim. (Cl. 17E-41.5)

Vernier variable condenser.

An object of this invention is to provide a Vernier variable condenser which is particularly adaptedfor use with precision apparatus.

Another object of this invention is to provide a Vernier variable condenser in which thev rate of capacity change will be substantially uniform throughout the full movement of the variable element.

In Vernier variabley condensers known in the priorl art, considerable trouble was frequently encountered in constructing and keeping the inner rod or Aelectrode concentric with the outermost cylinder, for the reason that any eccentricity of the inner rod electrode or conductor with respect to the outer electrode caused a variation in the rate of capacity change in one revolution of the operating handle.

An object of this invention is to overcome the above mentioned trouble by arranging the inner electrode so that it will not rotate. Therefore, if there is any eccentricity, it will not cause a variation in the rate of capacity change.

This invention will best be understood by referring to the accompanying drawings, in which Fig. 1 is a longitudinal section of one embodiment of this invention;

Fig. 1a is a rear elevation of Fig. 1;

Fig. 2 is a longitudinal section of another embodiment of this invention;

Fig. 3 is a son further embodiment of this invention;

Fig. 3a is a cross-section of Fig. 3, the section being taken on lines a-a; and

Fig. 4 is a. longitudinal section of still another embodiment of this invention.

v trode I and may be composed of a metal sleeve supported on a quartz rod 3, or, if desired, electrode 2 may be a silver coating upon the quartz rod 3, or it may be formed integral with a guide head 4 which, as shown in the drawings, supports electrode 2 which telescopes over one end of the quartz rod 3. An insulating collar 5 is arranged on the threaded ends of rods 6 for supporting the ilxed electrode I and is secured thereto by means of a plurality of nuts 6a. A metal sleeve 'l is threaded on the rearmost portion of electrode I and serves to retain a spring 9 which keeps the guide head 4 against the spindle of a micrometer head 8which micrometer head is similar in construction to the ordinary machinist's micrometer, and is described in detail in theUsselman and Franklin application, filed June 27, 1939, S. N. 281,344. Themicrometer head is secured to plate I0 which, in turn, is fastened to panel II by means of screws IIIa. The condenser capacity is varied by moving the barrel of micrometer 8 which, in turn, rotates the spindle 8a and causes guide member 4 to move electrode 2 into electrode I. Outward movement to decrease the capacity of the condenser is accomplished by means of the expan-` sion of a spring 9 which is interposed between member l and a ilange 9a located on rod 3. The inner electrode 2 is held concentric to the fixed electrode I by guide head 4 at one end and a bearing plate I2 at the rear end of electrode I. The modication shown by Fig. 2 is somewhat similar to that of Fig. 1, except that the guide rods 6 are dispensed with and a flange-like member 24 is substituted therefor. The fixed metal electrode 2| is secured to ange member 24 by means of an insulating support member 25. The movable electrode 22 is also in the form of a metal sleeve on quartz rod 23 and is so arranged that the support member 25 has a portion of its wall interposed between metallic elecis secured to a panel 20 by means of a plurality of screws 20a. A metal sleeve 29 carries a spring 21 and is secured to electrode 2| by means of screws 29a. Spring 2l is arranged to always force the quartz rod 23 against the spindle o1 the micrometer through aball bearing member 30.

The embodiment shown by Figs. 3 and 3a is generally similar to that of the construction shown in Fig. la, except that the rods 6 are also dispensed with and in their place is substituted a tubular slotted kmember 36. Member 36 Is arranged to guide the movable electrode 32 concentric with the xed electrode 3| which is composed of any suitable metal having a low coefficient of thermal expansion. Movable electrode 32 is in the form of a metal sleeve or coaty ing upon a quartz rod 33. Member 32a is in the 'form of a cylinder which slides in the slotted guide cylinder 36. An insulating ange-like co1- lar 35 is fitted into the slotted cylinder member rear end of insulating rod 33. A micrometer head 38 is fastened to a plate 40 by means of screws 40a to the mounting panel. The foremost end of the metallic sleeve 32 is provided with a rod-like portion 32a having located therein guide pins 32h, which ride in the slots of member 36. Electrical connection for the condenser is made at terminals 35h and 3217.A The electrical connection leads are indicated by arrows connected to members 35h and 32h.

The other form of vemier variable condenser is shown by the sectional view of Fig. 4`and comprises a fixed electrode 4| of a metal having low temperature coeiilcient lof thermal expansion, such asINVAR, and located concentrically therewith is a movable electrode 42 of 'similar metal. A metal shell 43 serves as a cylindrical piston chamber in which the piston-shape movable eleccondenser to the panel 41 and carries an insulator trode 42 works. Member 43 alsosupports the 44 in which ilxed electrode 4I is placed. Member 44 may be of fused quartz to increase the.

capacity of the condenser so that electrodes 4| and 42 maybe made much smaller than one in which the dielectric is only that of air. Movable Aelectrode 42 is actuated by the micrometer 48 to increase the condenser capacity and a spring 45 is provided to decrease the condenser capacity.

Although only a few embodiments of this invention has been shown, it is to be distinctly understood that this invention `should not be limited to the precise arrangement shown.

What is claimed is: A -variable condenser comprising a cylindric slotted guide member, an insulating member secured to said slotted guide member, a fixed electrodesecured to said insulating member, an insulating rod supported by said fixed electrode, a movable electrode secured to said insulating rod', one end of said movable electrode having guide pins to `slide in the slot of said slotted guide member, and means to vary the condenser capacity by movement of said movable electrode Within said fixed electrode.

' RALPH E. FRANKLIN.

EARLE DAYTON T HORNE. 

